Optimizing the Chloroallene Pathway Toward the One-Pot Synthesis of Rubrene

Abstract

Rubrene, a benchmark organic semiconductor, is commonly synthesised from 1,1,3-triphenylpropargyl alcohol (TPPA) via the key chloroallene intermediate (TPCA) through a one-pot protocol whose efficiency is highly sensitive to the TPPA-TPCA conversion conditions. We show that treatment of TPPA with PCl₅ in the presence of base affords up to 85% TPCA formation (HPLC), but optimization of the subsequent high-temperature step is hampered by competing pathways leading to cyclobutene by-products, which complicate purification and limit the robustness of a truly one-pot process. Guided by these observations and by reports on trimethylsilyl chloride (TMSCl)-mediated propargyl–allenyl rearrangements, we developed an alternative TMSCl-based protocol. The combination of TMSCl with a sterically hindered base enables a markedly cleaner one-pot synthesis, delivering rubrene in 68% yield by UV-Vis analysis and 61% yield of isolated product, with complete suppression of cyclobutene formation and a greatly simplified workup. This study provides a rational framework for controlling the chloroallene reaction manifold and establishes a more practical and reproducible one-pot route to rubrene.